For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

Vehicle Care
California Proposition 65 WarningInstallation Procedure
Align the front side door outer panel.
Verify the fit of the front side door outer panel.
Clamp the front side door outer panel
into position.
Pre-flanging the flange with BO-6396 pliers and BO-6392 tool kit .
Continue to hammer in stages along the hem flanges.
...
Installation Procedure
Align the body side outer panel reinforcement.
Clean and prepare the attaching surfaces for welding.
Position the body side outer panel
reinforcement on the vehicle.
Verify the fit of the body side outer panel reinforcement.
Clamp the body side outer panel reinforcement ...
Doing Your Own Service Work
WARNING
It can be dangerous to work on your vehicle if you do not have the proper
knowledge, service manual, tools, or parts. Always follow owner manual procedures
and consult the service manual for your vehicle before doing any service work.
If doing some of your own service work, use the pro ...